1. Field of the Invention
The present invention relates to an elastic wave device, such as a surface acoustic wave device, and a manufacturing method for the elastic wave device. More particularly, the present invention relates to an elastic wave device that includes wiring electrodes electrically connected to IDT (interdigital transducer) electrodes, and also relates to a manufacturing method for the elastic wave device.
2. Description of the Related Art
From the viewpoint of reducing the size of an electronic device, size reduction of a surface acoustic wave device has also been strongly demanded so far. The surface acoustic wave device is required to include a hollow portion constituted such that IDT electrodes are positioned to face the hollow portion. Under such a situation, Japanese Unexamined Patent Application Publication No. 2010-278971 intends to reduce the size of a surface acoustic wave device including a hollow portion. In Japanese Unexamined Patent Application Publication No. 2010-278971, the IDT electrodes are formed on a piezoelectric substrate. A support layer is disposed on the piezoelectric substrate and surrounds a region where the IDT electrodes are formed. A cover layer serving as a cover member is laminated to cover an opening in the support layer. With that structure, size reduction is realized. A through-hole is formed in the support layer by, e.g., a laser. An under bump metal layer is filled in the through-hole. The under bump metal layer is connected to an underlying electrode.
On the other hand, in a surface acoustic wave device disclosed in Japanese Unexamined Patent Application Publication No. 2003-174056, wiring of two-layer structure is disposed in a partly overlapping relation relative to the IDT electrodes. Japanese Unexamined Patent Application Publication No. 2003-174056 states that cracks generated between the piezoelectric substrate and the IDT electrodes can be suppressed with the above-mentioned feature. In the wiring of two-layer structure, an upper electrode layer is formed of an Al film.
In the surface acoustic wave device disclosed in Japanese Unexamined Patent Application Publication No. 2010-278971, the through-hole is formed in the support layer with irradiation of a laser beam, for example, and the under bump metal layer is formed in the through-hole. In that structure, there is a risk that, when the through-hole is formed, an electrode surface exposed under the through-hole may have its properties altered. In particular, when, as disclosed in Japanese Unexamined Patent Application Publication No. 2003-174056, the two-layer wiring structure including the Al film on the upper surface side is used as a wiring electrode that is connected to the IDT electrodes, there is a risk that the Al film may experience altered properties due to the irradiation of the laser beam. Moreover, the Al film has a natural oxide film on its surface. This causes another problem that when a via conductor, such as the under bump metal layer, is formed by a plating method, a plating film is hard to adhere to the Al film.